1. Field of the Invention
This invention relates to a printed loop antenna with introducing a L shape portion to its arms for Ultra Wideband (UWB) signal radiation.
2. Description of the Related Art
The main difference between UWB communication system and conventional narrowband communication systems is that the UWB system transmits tremendously short pulses without any carrier and occupies bandwidth of more than a few GHz. As a result, the antenna plays an important role in the UWB systems than it in any other system.
Compare to traditional antennas it is more complicated to provide the typical parameters like bandwidth and gain within the limited antenna volume. An antenna design becomes even more critical with respect to the UWB system with high data rate and low power density. Moreover, antennas for the UWB system should have linear phase over the entire frequency, omni-directional patterns, and constant gain. Therefore, UWB antenna should be designed carefully to avoid unnecessary distortions. That's why the UWB antenna design is going to be one of the main challenges for UWB system.
Printed monopole and dipole antennas are extensively used in different wireless applications due to their many advantages, such as low profile, light weight, easy to fabricate and low cost, some of them are references [1]-[2].
The loop antennas also can be used for wireless communications (references [3]-[5]).
FIG. 11 shows a loop antenna of a prior art. On the top of a substrate 1, a single metallic layer, which is copper, is printed. However, a conventional wire loop antenna shows less than 10% bandwidth for a 2:1 VSWR. Therefore, conventional loop antenna went under different modifications to increase the bandwidth. A broadband loop antenna has been introduced by reference [3], which have a small gap in the wire loop. This small gap increased the impedance bandwidth to more than 24%.
In this invention we present a loop antenna whose left and upper arms together introduce an L-shape. However, the L-shape antenna itself is a class of broadband planar antenna, which allows the broad impedance bandwidth and less cross-polarization radiation (references [6], [7]).